Direction finding system



1950 P. G. HANSEL DIRECTION FINDING SYSTEM Filed Oct. 16. 1945 mmDk m 2mo;

Illlllllg L E o m m m T N M E V 0 m L REG P 5016 u E5 E5 m 3b N1 on mm m0; 2w m fllllllllll mu w #9 n 4 523mm 928 m1 EEim umii OE ApplicationOctober 18, 1945, Se l No. 622,64d

18 Claims. (Cl. 343-118) (Granted under the act of rent, 1883. asamended All? 30, 928; 370 G. 757) The invention described herein may bemanu- This is a carrier-suppressed signal which is lec ed a d used y forthe Government directionally characterized in that the direct'andovernmental P poses, without the P y reciprocal directions of arrivalare implicit in its me of y oyalty ther nenvelope phase. A substantiallyidentical signal This invention pertains to radio direction find- 5might be obtained by spinning a single vertical i systems and as p icu rappli abi ity t loop antenna about a vertical axis. those of the directreading type. A reference antenna R is connected to the The inventi n isn ally appli a l to d r or receiver input through a phase-shifter is toprotlon finding y m wh rein a ir c n vide a carrier signal es which isnot directionally tenna sys is a ually, or in i en c i uous locharacterized and which is of the form: rotated to produce adirectionally-characterized e t (2) signal whose modulation phase is afunction of cos the direct and reciprocal directions of wave Such asignal is commonly employed in convenarrival. tional systems forsense-finding purposes. In

An important object of this invention is to s this invention the carriersignal e0, expressed by provide a convenient method whereby both theEquation 2, although it may be used for sense signal sensitivity and theobservational accuracy findin also serves another purpose, namely to ofa direction finder may be enhanced. i dist rt the envelope symmetry ofthe direction- A further object is to provide direction findinally-characterized signal ed without regard to the systems of extremelyhigh observational accuracy 8 1158 or direction of the distortion. foroperation over limited azimuthal sectors. The amplitude of the carriersignal err is made Another object is to provide a direction mrless thanthe maximum amplitude of the direcing method whereby accurate bearingobservalonallycharacterized signal ea so that the envetions may beobtained under diflicult conditions lobe of the resultant signal (ea+ec)which is imsuch as those imposed by rapidly-varying spacepressed uponreceiver I9, is a degenerate cardioid diversity eilects and multiple-rayreception. when plotted in polar coordinates.

For a better understanding or the invention Th output of rece er I9 is apulsatin s nal together with other and further objects thereot, having"nulls or minima which are unsymmetreference is had to the followingdescription rically d sp in time- This Output 18 1111- taken inconjunction with the accompanying pressed upon a modulator 2| tomodulate, prefdrawing, wherein: erably negatively, a moderatelyhigh-frequency Figure 1 is a block diagram of one embodiment signalderived from a deflection signal source 20. of this invention; which maybe a sine wave oscillator. The modu- Figure 2 is a schematic circuitdiagram of a lated output of modulator 2| is impressed uponspaced-aerial arrangement for deriving a referthe beam deflec in means22 associated with a ence signal which is not directionallycharaetercathode ray tube 24 to produce a diametral line ized to asignificant degree; trace, the length of which is controlled by theFigure 3 shows a typical double propeller indioutput of receiver is. Thebeam deflection means cating display; and 22 may take the form of arotatable deflection Figure 4 shows the unsymmetrical form of indl- 9coil.

cating display obtained under conditions uniavor- Rotator I5 i coupled hbeam d flection able for direction finding. means 22 to produce rotationof the diametral Referring particularly to Fig. 1, aconventional linetrace at an angular velocity equal to an direction findingantenna systemto, which comintegral 1' fractional multiple of the u a prises thespaced aerials N, E, s, and w arranged as ve oc ty o e onlo e e rota on,d pendin at the corners of a square, is coupled to a goniup the p p earatio of the gear ometer l2. The latter is continuously driven Sy winterposed we n h ro ator and through a gear system l8 by a rotator i6,which the goniometer.

may be a y The gonlometer output is The resultant pattern which appearson the pressed upon a receiver a9, screen of the cathode ray tube 24will be of the As is n known t signal ed bt g form shown in Fig. 3.Under favorable conditions the gomometer is of the form; pattern willconsist of tWO identical propelers w ose angular displacement dependsupon cos ("FWD cos (n 4 the ratio of the carrier signal co to thecarrierwhere in is a constant, '55 suppressed signal ed. Theintersection of the two a is the direction of wave arrival,singularly-displaced propellers represents the we is the angularfrequency of the-received bearing and can be read with the aid of analidade signal, and to a much higher degree of precision that can thewristhe angular velocity of the goniometer 'aar position of a singlepropeller. This is rotation. $0 an advantage which is particularlyimportant when the received signal is so weak that the tips of thepropellers are obscured by noise traces. It has been found in practicethat the most favorable ratio of co to en is about 0.5 although a ratioup to unity might be used.

This method of producing split presentation is superior to the manualsplitting method disclosed in my co-pending ap lication, entitledReceiving apparatus," Serial No. 541,950, filed June 24, 1944, issued onJuly 26, 1949 as Patent No. 2,476,977, because it requires nomanipulation of controls on the bearing indicator and because, inaddition, it increases the actual amount of signal received, therebyenhancing the signal sensitivity as well as the observational accuracy.As workers in the field of short-wave direction finding are aware, manysignals encountered in practice exhibit violent and almost continuousfluctuations in the apparent direction of arrival. Under theseconditions accurate reading of bearings is practically impossible withconventional direction finders. Through the use of this invention,however, bearings can usually be obtained under such conditions with ahigh degree of accuracy. The reason for this is that thesymmetrically-split pattern shown in Fig. 3 is produced only when thephase relation between the directionally-characterized signal ed and thecarrier signal e is in accord with Equations 1 and 2. When, for example,space-diversity effects produce severe wavefront distortion, anunsymmetrically-split pattern such as that shown in Fig. 4 will beproduced. The operator is thereby warned that the bearing is unreliableand he can then wait until the pattern becomes symmetrical beforerecording a bearing observation. The symmetry characteristics of thepattern thus provide a convenient criterion for distinguishing betweenfavorable and unfavorable times for recording a bearing. Even betterperformance in this regard can be obtained by eliminating the referenceantenna R and the phase shifter l4 and utilizing as the required carriersignal e0 the differentiated outputs of any even number of spacedaerials. This can be accomplished in the manner shown in Fig. 2. Thespaced aerials 28 and 30, which may be two of the aerials N, S, E, andW, are connected to differentiating circuits 32 and 34 respectively. Theresulting difierentiated signals are combined to produce a carriersignal on which may be impressed upon the input of receiver M in placeof the phase-shifted output of a single reference antenna as previouslyshown in Fig. 1. Since'the phase of a signal resulting from thecombination of an even number of signals derived from spaced aerials iscritically dependent upon the relative amplitudes of the componentsignals, wavefront distortion will result in extremely pronounced lackof pattern symmetry.

Direction finding applications exist which require an observationalaccuracy or repeatability of, for example, fig-degree. Usually in suchapplications operation is required over only a limited azimuthal range.The observational accuracy obtainable with most conventional directionfinders is only in the order of one degree. As previously stated, one ofthe objects of the present invention is to provide direction findingsys-- tems of extremely high observational accuracy. This isaccomplished in the following manner: As shown in Fig. 1, a gear systemIt is connected between the rotator l8 and the goniometer l2.

By employing a step-down ratio of, for example, 10 to 1, it is possibleto rotate the beam deflection means 22 at an angular velocity of tentimes the angular velocity of the goniometer. Thus the azimuth scale ofthe cathode-ray tube 24 is expanded so that the full 360 mechanicaldegrees actually represent only 36 degrees of azimuth. Each degreemarker on the scale will then represent only f -degree. With theconventional single propeller presentation, expansion of the scale alsoresults in such severe blunting of the propeller tips that the effectiveimprovement in observational accuracy is much less than the scaleexpansion factor. On the other hand, with the split-propellerpresentation provided by this invention, it is possible to realize thefull improvement in'observational accuracy corresponding to the scaleexpansion factor.

Scale expansion results in sectoral ambiguity which can be resolved bymaking the ratio of the gearsystem I8 variable. For example, a gearratio of 1 to 1 could be employed to determine the sector and then aratio of 10 to 1 could be employed to permit high-precision observationof bearing. The gear system I8 is shown adjustable for this purpose.

This invention is readily applicable to direction finders of the typedisclosed in my co-pending application above cited, the disclosure ofwhich is hereby made a part of this application. For this purpose,switches 5|, 52, 53, and 54 shown in Figs. 1 and 8 of said application,should be closed. The four resistors shown in said Fig. 8 should beadjusted to provide a ratio of ea to 8d of about 0.5. The blankingswitch shown in Fig. 2 of said application should be open. Theabovedescribed method for applying the present invention to thedirection finder shown in said copending application is also disclosedin Electronics, April 1948, pages 86-91.

' Scale expansion can be readily applied to the direction finder of saidapplication by interposing a frequency multiplier, which is preferablyvariable to provide any desired degree of multiplication, between thephase rotation control 40 and the amplifier and filter 4| shown in Fig.2 of said application.

While there has been described what is at present considered a preferredembodiment of the invention, it will be obvious to those skilled in theart that various changes and modifications may be made therein withoutdeparting from the invention, and it is aimed in the appended claims tocover all such changes and modifications as fall within the true spiritand scope of the invention.

I claim:

1. A direction finding system comprising: an antenna system withassociated effective rotating means for deriving from a single incomingwave -a directional]y-characterized signal whose modulation phase is afunction of the direct and reciprocal directions of wave arrival; meansfor deriving from said wave a carrier signal; continuously receptivemeans for combining said firstnamed signal with said carrier signal toobtain a resultant directionally-characterized signal having envelopeminima unsymmetrically displaced in time; a radio receiver to which saidresultant signal is applied; and indicating means receptive of theoutput of said receiver for producing intersecting indicia having anangular displacement proportional to the relative magnitudes of saidcarrier signal and said first-named signal.

2. A system as set forth in claim 1, wherein said means for deriving acarrier signal is a nondirectional antenna means.

3. A direction finding system comprising:

as ,esa

tube; means for deflecting the beam of said cathode ray tube to producea diametral line trace; means for rotating said diametral line trace atan angular velocity of U1 and means for controlling the instantaneouslength of said trace in accordance with the output of said receiver toproduce a pair of intersecting propeller-shaped indicia having anangular displacement proportional to the relative magnitudes of saidfirst and second signals.

4. A direction finding system according to claim 1, wherein said meansfor deriving from said wave a carrier signal comprises an even number ofspaced antennas.

5. A direction finding system according to claim 3, wherein saiddiametral line trace is rotated at an angular velocity equal to anintegral multiple of air.

6. A direction finding system according to claim 3, wherein said secondsignal is derived from an even number of spaced antennas.

7. A direction finding system according to claim 3, wherein said secondsignal is derived from an even number of spaced aerials and wherein saiddiametral line trace is rotated at an angular velocity equal to anintegral multiple of we.

8. A direction finding system as set forth in claim 3, wherein the meansfor obtaining said second signal comprises an even number of spacedantennas, means for separately difierentiating the output of each ofsaid antennas, and means to combine the differentiated outputs.

9. A direction finding system for radio waves comprising: antenna meansto derive from a single incoming wave a pair of signals, one signalbeing independent of the bearing of said incoming wave, the other signalhaving a modulation superimposed thereon, the phase of said modulationbeing dependent upon said bearing but having 180 ambiguitytherein,.-means for combining said signals to derive a resultantmodulated signal having a modulation phase which is dependent upon saidbearing and has 180 ambiguity therein, said resultant signal having aplurality of minima unsymmetrically displaced in time, and indicatingmeans continuously responsive to said resultant signal for pradueingintersecting indicia having an angular displace= ment dependent upon therelative magnitudes of said pair of signals.

10. A direction finding system comprising: directional antenna means,means for producing a rotation of the effective direction of saidantenna means, means responsive to said rotation for deriving from anincoming wave of modulated sigdependent upon said bearing and having aplurality of minima unsymmetrlcally displaced in time, a cathode raytube, means for deflecting the beam of said tube to produce a diametralline trace, means synchronized with said rotation for rotating saiddiametral line trace, and means for controlling the instantaneous lengthof said trace in accordance with the instantaneous amplitude of saidresultant signal.

11. A directionfinding system as set forth in claim 10, wherein saidinstantaneous length is inversely proportional to said instantaneousamplitude.

12. A direction finding system as set forth in claim 10, wherein saiddiametral line trace is rotated at an angular velocity which is equal toan integral multiple of the angular velocity of said rotation.

13. A direction finding system as set forth in claim 10, whereinsaidsecond signal is derived from an even number of spaced antennas.

14. A direction finding system as set forth in claim 13, wherein saidspaced antennas constitute part of said directional antenna means.

15. A direction finding system as set forth in claim 10, wherein themeans for deriving said second signal comprises an even number of spacedantennas, means for separate difi'erentiating the output of each of saidantennas, and means to combine the differentiated outputs.

16. A direction finding system comprising a directional means forderiving from an incoming wave a signal having a fixed angular frequencyand a direction-dependent phase, a phase meter having periodicallymovable indication producing means responsive to said signal toindicatesaid phase, the frequency of said periodically sponsive to said signalsto indicate said phase, the

angular frequency of said rotatable means being an integral multiple ofsaid fixed angular frequency.

18. A system according to claim 17, including means for altering saidmultiple.

PAUL G. HANSEL.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNZiTED STATES PATENTS Number Name Date 1,908,006 Belline May 9, 19332,213,273 Earp Sept. 3, 1940 2,238,129 Paul Apr. 15, 1941 2,263,377Busignies Nov. 18, 1941 2,297,414 Janovsky Sept. 29, 1942 2,314,093Landon Mar. 16, 1943 2,380,929 Ahier etal Aug. '7, 1945 2,388,262Ganiayre Nov. 6, 1945 2,403,727 Loughren July 9, 1946 2,403,967Busignies July 16, 1946 2,405,203 Goldstein Aug. 6, 1946 2,407,281Johnson et al Sept. 10, 1946 Certificate of Correction Patent No.2,494,553 January 17, 1950 PAUL G. HANSEL It is hereby certified thaterror appears in the printed specification of the above numbered patentrequiring correction as follows:

Column 5, line 64, for the words wave of read wave a;

and that the said Letters Patent should be read with this correctiontherein that the same may conform to the record of the case in thePatent Office.

Signed and sealed this 2nd day of May, A. D. 1950.

THOMAS F. MURPHY,

Assistant Oommz'saz'oner of Patents.

